PC Power supply

[SteveRosenlund]

Hello all,

I've already ordered a replacement, but i want to play with this PSU for my PC that turns on, sends out the correct voltages, but doesn't provide full power before shutting off. 
It started with my kids complaining that the computer keeps shutting off on its own.  My oldest son blew out the dust from the case, CPU fan, PSU, etc and it was slightly more stable but still shut down periodically.  I removed the PSU, took it to my lab, and took it apart.  using my Rigol DL3021 load, I stress tested the 12 volt rail and it will only supply 150w before shutting off completely.  Also, the voltage drops to 10v under loads over 100w.  I took some thermal pictures to show which componenets are heating up the most.  I'd appreciate any help or advice you can give me on where to go next.  I'm still new enough to not really know how to trouble shoot these things or trace signals.

Here's the basics:
Thermaltake cheap power supply 500w rating.
DC Output specs:
3.3v 22A
5V 18A
+12V1 18A
+12V2 17A
-12V 0.3A
+5VSB 2.5A








Steve

[Manul]

You did these measurements without a cooling fan? 243F temperature? That is way too much. You should have a fan for 500W psu.

Does it give more power if you cool it really good with a strong fan?

Would also be interesting to measure efficiency, input power vs output power.

[M0HZH]

That looks cheap.

You need to load the 5V rail (1-2A) or rework the internal feedback circuitry if you want to get full output on the 12V rail.

Q7 seems to be run very hot, worth starting from there.

JunFu capacitors might have dried up, woth testing as well.

[wraper]

FWIW this PSU is trash which is slightly above the worst PSUs you can possibly buy. 500W rating most likely is fake. Not worth repairing unless you are desperate. I'm surprised Thermaltake sold it under their name.

[SteveRosenlund]

You did these measurements without a cooling fan? 243F temperature? That is way too much. You should have a fan for 500W psu.

Does it give more power if you cool it really good with a strong fan?

Would also be interesting to measure efficiency, input power vs output power.

No I pulled the case top and fan off right after measuring before shooting with FLIR

At the wall it pulls 108w when running a 75w load on the PSU.

Thanks for the reply!

[SteveRosenlund]

FWIW this PSU is trash which is slightly above the worst PSUs you can possibly buy. 500W rating most likely is fake. Not worth repairing unless you are desperate.

Yeah I know it’s cheap.
Like I said I already ordered a replacement, this is just for fun

[SteveRosenlund]

That looks cheap.

You need to load the 5V rail (1-2A) or rework the internal feedback circuitry if you want to get full output on the 12V rail.

Q7 seems to be run very hot, worth starting from there.

JunFu capacitors might have dried up, woth testing as well.

Thanks for the guidance. I’ll load the 5v rail and retest when I get time. I’ll also test the caps. I did notice q7 and replaced it. It was an npn transistor. I had one of the same value in my inventory.

[Manul]

That looks like a decreased efficiency. And thermal shutdow is natural consequence.